Method of starting synchronous polyphase motors.



3,1. FECHHHMER. METHOD OF STARTING SYNSHRONOUS PGLYPHASE MGTORS.

Paientad Jan. 18, 916..

a APPLICATEON FILED MAY 6, 3913. i,i8,383

2 SHYEETS-SHEET 1.

.IIWEAITGH jaw .- win/8858 6.1. FECHHEIMER. METHOD OF STARTING SYNGHRONOUS POLYPHASE MOTORS APPLICATION mm MAY 6, 1913. 1,168,383.

2 SHEETS-SHEEI 2.

WITNESSES I m l/mml? BY M W. Gwzrkeg;

Patented Jan. 18, 1916.

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unrrn n s rn'rns ra'rnutr OFFICE.

CARL J. FECHHEIMER, OF GLEN RIDGE, NEW JERSEY, ASSIGNOB '10 GROCKER- WHEELER COMPANY, OF AMPERE, NEW JERSEY, A CORPORATION OF NEW JERSEY.

METHOD OF STARTING SYNCHRONOUS POLYPHASE MOTORS.

Specification of Letters Patent.

Batented Jan. 18, 1916.

Application filed May 6, 1913. Serial No. 765,862.

To all whom it may concern: v Be it known that I, CARL J. Fronnnnrsn, a citizenof the United States, and" trio motors.

In accordance with my invention I apply to the armature of such a motor one or more voltages which are fractions of the working voltage and may be "conveniently obtained autotransformers, then I excite the field, after which inductive reactance is introduced into the armature circuit and finally the full voltage is im- By my method the motor is started and brought up to synchronism in a very satisfactory manner; at the same time I am able to accomplish this without interrupting the supply of current to the armature and without the use of preventive resistance or reactance usually employed. l/Vhen my method is used, a synchronous time draw a large amount of current in starting, the maximum current being much 'less than it is with the methods heretofore employed.

My invention may be applied to singlephase, two-phase, three-phase, four-phase, six-phase, or to any bthersynchronous alternating current motors, including rotary converters. Moreover it is applicable to various modified arrangements of each the star or Y connection as well as the delta, nected three-phase arrangements;

In the accompanying drawings which illustrate several of these different arrangements by which my invention may be practised: Figure 1 shows one of the simplest combinations of apparatus and circuits for starting a three-phase synchronous motor, making use of two auto-transformers connected in V relation Fig. 2 represents the arrangement that may be adopted to start a three-phase synchronous motor utilizing Y connected autotransformer-s; Flg. 3 shows another three-phase modification employ- 'ing autotransformers connected 111 delta;

useful Improvethe V and the T con-- Fig. 4also shows a threehase motor which is started by means of T connected autotransformers; Fig. 5 represents a two-phase, synchronous motor arranged to be started in accordance with my invention; and Fig. 6 represents the application of my invention to-the starting of a single phase, synchronous motor.

In Fig. 1 the circle marked M indicates the. armature, usually the stator, of a three-' phase synchronous motor that is to be started; F is its field winding, usually on the rotor; R is a rheostat in series with the field to regulate the exciting current therein; S 1s a switch that opens or closes the field'cir suit and- E is a dynamo electric ex'citer orthe armature M being the switches by which the connections are controlled, their operation beihg fully explained later.

Three line wires their connection tothe In order to start the motor according to my invention, the switch S is open so that there. is no current to excite the field. The switches 3 and 4 are closed and the switches 1 and 2 are open. Two leads of the armature winding of the motor are, connected to two taps of the autotransformers, respectively. The third armature lead is connected directly to the supply wireY. lVith these connections one half or any other suitable fraction of the line voltage is impressed upon the armature M of the motor in the customary manner. The motor thereupon starts and comes up to speed, locking into synchronism and drawing the usual lagging current. The field F of the motor is then excited by closing the switch S, the current in the field being suflicient to over excite it with the fractional voltage impressed upon the armature, having approximately the value employed for operating the motor at normal voltage with about 100 per cent. power factor. This over excitation of the field advances the phase of the armature current, and the armature tends to draw a the motor would cient torque to leading current, this causes the voltage to rise at the armature terminals until the current falls to a c0m- I n the foregoing description it was I is shown in Fig. 2.

autotransformers, the inductive reactance of the two coils A andv B in series with two of the armature leads, respectively. In asmuch as the armature tends to draw a inductive reactance parativ'ely small. value, the power factor approximating unity and the counter ll]. F. being about equal to the line voltage. There may be, however, some time-phase difiier- 'ence between the E. M. F. at the armature terminals and that of the line, but the difference in phase? orin magnitudeis not cient to cause any material disturbance when the switches l and 2 are now closed. The motor is thus-connected directly to the line, the whole operation having been ac complished without at any time cutting off the current to the armature even momentarily. 1

stated that the motor would pull into synclironism with a fraction of the line voltage. The characteristics of the'load may be such that not be able to exert sufficlose with the particular fractional voltage. Under these conditions the eiicitation of the field which is the next step in the operation of starting, will usually cause the motor to lock into synchrouism. In case, therefore, the motor does not get into step before the field icf'excited it should certainly do so afterward.

One of the distinct advantages of my method is that it insuresthe correct polarity of the rotor poles after the motor comes into synchronism when the'direct current is a plied to the field before synchronism is reached. If it is applied afterward and the polarity is not already correct the motor would slip a pole in order to bring the M. M. F. of the stator and that due to the direct current in the rotor into the proper relation. This readjustment will not, how-- ever, create nearly as. much line disturbance as would be thecase it. :fnllline voltage were applied to the armature before the field is excited. As maximum current drawn at any time is not very large, being seldom more than that re quired to start-the motcrirom when it is started in accordance with my method.

The application of my invention to the starting of a synchronous three-phase motor by means of Y connected autotransformers As in all the IS the armature and F the field winding; of the motor. There are three autotransformers, each having one terminal, (or an adjustable intermediate point as indicated in Fig. 2) connected to one of the supply lines already stated, the

incense spectively connected to the lines X, Y and. Z by switches 5, 9 and l and to intermediate points of the three autotransformers by switches 6, 8 and 11, as clearly indicated in Fig. 2. In order to start the motor, switches 6, 8, 11 and 10 are closed While switches S, 5, 9 and 12 are open. With these connections the armature lvl has impressed upon it a suitable fraction of the line voltage, the effect of which is to start the motor and bring it up to or near synchronisin. The field is then excited by clos in the switc S, the field current being sniiicient to overexcite the field with the fractional voltageimpressed upon the armature, so that the latter draws a leading current, as in the previous case. The switch 10 is then opened breaking connections at 7,

and introducing into the three armature cirdelta connected autotransformers, according to my invention. As before M is the armature, F the field winding and there are three auto-transformers each having one terminal connected to one of the three-phase supply lines X, Y and 23, respectively. In order to start the motor, the double-throw switches 13, and 22 are closed in the position shown, which completes the delta connection of the three autotransformers. The three switches 16, 19 and 23 are also closed, thereby impressing a proper fraction of line voltage upon the armattlre M of the motor which starts and comes up to or approxi mates synchronism. The field is then excited by closing switch 3, after which the double throw switches are opened at 13,-17 and and closed at 15, 18 and 20, thus connecting the armature M directly to the armature to the starting of a two-phase synchronous motor is represented, M being its armature and Fits field winding with a suitable exciter E,rheostat R and circuit-controlling switch S, as in the case of the three-phase motors already described. One terminal 32 of an autotransformer is connected to one of the lines G of one phase of the circuit, and one terminal 35 of the other autotransformer is connected to a line J of the other phase of the two-phase supply. 'To start the motor the switches 33, 34, 36 and 37 are closed, 32 and 35 being open, whereby an appropriate fraction of the line voltage is im pressed upon the armature M. After the rotor has accelerated until it reaches or approximates synchronous speed, the field F is excited by closing the switch S. Then the switches 34 and 37 are opened thereby introducing the impedances 32, 33 and 35, 36 into the armature circuit, after which the switches 32 and 35 are closed to connect the armature M directly to the two-phase supply lines. In this case as in the others, the

starting is accomplished according to my invention without opening the armature cir-- cuit and with minimum current and disturbance in the motor or line.

In the drawings I have not shown switches that will entirely disconnect the autotransformers and motors from the supply circuits,

because it is obvious that they could bein- 'troduced if desired. For the sake of simplicity I have represented only those switches that are actually employed in carrying out my invention. Of course, the various well-known switching, controlling and regulating devices, circuit-breakers, fuses,

etc., may be introduced and used wherever and whenever they are desirable, in the manner familiar to those skilled in the art.

It is also evident that the proportions of 'the various autotransformers with their subdivisions and connections may be altered in the utilization of my invention without departing from it. For example, the taps A and B in Fig. 1, also the taps 6, 8 and 11 as well as those in other. modifications of my invention may be connected at any suitable points of the auto-transforme'rsto give the desired fractional voltages for starting, accelerating or operating the motors. Moreover it is also obvious that there may be two or more of these taps for each autotransformer to give two or more fractional -voltages. These tap-connections may also be arranged to be readily shifted or adjusted in position bv hand or automatically as indicated at A and B in. Fig. 1 and in the other figures, so as to change or regulate the fractional voltages obtained therefrom. The shifting of the position of these taps also has the effect of varyingthe values of the impedancesf introduced into the armature circuitduring the operation of starting. In

this Way their values may be altered or adjusted, if desired. These impedances may also be changed by shifting the positions of the connections 1 and 2 iii-Fig. l for exam-, ple, or the corresponding connections in other cases: In this way the impedancesas well as fractional voltages may be either mutually or independently varied *or regulated to any desired yalues. y I

The application of my method to the'starting of a single phase synchronous motor V which is represented in Fig. 6 is evidently similar to the case of the two-phase motor already described with reference to Fig. 5, the pair of supply conductorsand connecac tions belonging to one-phase being omitted. It is of course necessary to provide some means for starting the single-phase motor. For example an auxiliary direct current motor, which may be the eXciter E fed from a 83 storage battery, can be used. It is obvious that other means well known in the art may be used for this purpose. When the synchronous motor represented in Fig. 6 has been started and brought up to or near synchronous speed, the switches 39 and a0 being closed the field is excited by closing the switch S. The field current is of sufiicient strength to overexcite the field at the fractional voltage. The switch 40 is then opened thereby introducing the inductive reactance 38, 39 into the armature circuitwhich has the effects already explained. Finally the switch 38 is closed to connect the armature directly to the supply conductors.

It is evident that my invention -may be applied to rotary converters or other forms of apparatus which either wholly orin part consist of or embody synchronous alternat- 1, If such machines are .105

rying out the vai-ious modifications of my invention, but it is obvious that other well known means may-be substituted for autotransformers wherever desired Without (dc-1 parting from my claims. It is evident also that the inductive reactance introduced into the armature circuit may consist of coils .which are not part of the autotransformers.

Moreover these coils may or may ,not be around upon themagnetic cores of the autotlziIlSfOIIilQlS. Throughout this specification, I have em- I ployed in accordance with accepted .usage the term field magnet or simply field to 330 1 1c motor Wine} upuzi iis :wmzzh W3 viiiage, than degrbe flu d; 51,1112 cuz..mm, mm). cusz. from the fractions time ilm'nduciiug mum in i'iis (My k 50 19b 11%;, Eh :1 pp 1113mm m mn'ty and 171 sud macmnce and 0011111 ,1 ether ale/mam;

current WinC.-- I fies as electric motor which consists in impressing 11 p011 its armature a Tract-ion of the working voltage, than exciting the field to such a de gree that the HK'HHULUL'Q takes a leading curmnt, than disconnecting the armature from the fraciionai voltage and at the same time introducing sufiicient inductive reactrmce in its circuit se that the power factor approximates unity and finally cutting out said rencizance and connecting the armature direatly to the supply conductors, these Changes being effected Without interrupting the. armamu'e current.

Signed at Ampere in the county of Essex and. State of New Jersey this 2nd day of May A. 1913 CARL J. FEOIrIHEIMER.

Wi messes Dm/u) J. EIZAIIQLNEY, FRANCIS P). CROCKER. 

